1) Field of the Invention
This invention relates to Least Cost Routers for use in telecommunications. A Least Cost Router is a device for selecting, for a given communications call, one of a number of carriers (telecommunications service providers) depending upon variables such as cost. The cost of particular types of call, both national and intemational, varies from one carrier to another. An example in the United Kingdom is the price differential between British Telecom and Mercury Communications for different types of call. A Least Cost Router provides the facility for pro-programming which types of call are routed via which carrier. In this way, the user may simply select which types of call should be routed to which carrier and the call will automatically be routed by the cheapest available carrier.
2) Description of the Prior Art
A prior art call routing controller, known as Smart-1 .TM. is produced by Mitel .TM. Telecom Limited, of Gwent Wales. This device may be connected between the users extension and the local exchange, or a PABX and a local exchange, so that it may check each number the user dials. On recognizing a number, it may absorb some of the digits and replace them with previously stored digits to route the call via an alterative carrier, deny the call completely or record the start and duration of the call and print the information on an attached printer.
As an example, to connect to Mercury, three numbers must usually be sent. First a number telling BTs local exchange that you want to connect to the new network, then a customer identification number (PIN) and finally a number giving the address of the subscriber the user wishes to talk to, The process of dialling these numbers is laborious for the user and is circumvented by this prior art router. On installing the router, the phone number needed to reach the alternative network and the pin are stored within the device. These numbers may then be sent to the local exchange automatically by the router when the user dials a number on the telephone.
In addition to call routing, this unit provides a number of memories so that telephone numbers may be stored in the memories and accessed by the user dialling a shorter code on the telephone. Dialling of the pre-stored number is then initiated simply by dialling the short code. This feature must be preprogrammed, and the code supplied to the user so that the user has a list of short codes which may be dialed to initiate the calling of a particular telephone number. This is similar to memory stores known in telephones and facsimile machines.
There are further disclosures which provide background to the present invention. IEEE International Conference on Communications 1985 discloses a system of overlap outpulsing in which digits are always regenerated without connecting a terminal and network. Dialled digits are sent when the end of dialling is reached. Such digit regeneration is also disclosed in GB-A-2218595 in which all digits dialled by a terminal are regenerated and reconnects a terminal blindly after an arbitrary timeout.
Digit analysis is disclosed in EP-A-0,540,258 which also discloses monitoring for a dial tone before sending digits. Access codes are disclosed in U.S. Pat. No. 4,791,665 in which access codes are sent to an exchange.
A line pool is disclosed in U.S. Pat. No. 4,797,915 which discloses routing amongst a predetermined pool of lines.
We have appreciated problems with all such prior systems.